Mattress



FIG. 1 is a top, rear, and left side perspective view of a mattress according to the new design;

FIG. 2 is a top plan view thereof, the bottom view being a mirror image of that shown;

FIG. 3 is a left side elevation view thereof; the right side being a mirror image of that shown; and,

FIG. 4 is a rear elevation view thereof; the front being a mirror image of that shown. 

The ornamental design for a mattress, as shown and described. 